There has been proposed a supercharged 4-cycle engine, for example, such that a connecting rod housing chamber surrounded by a crank chamber, a crank web, and a piston is partitioned by a connecting rod into a suction chamber and a compression chamber so that the air sucked through the rocking of the connecting rod is compressed to be supercharged into the combustion chamber (see Japanese Patent Application Laid-Open No. 6,93869).
A suction device for such a supercharged engine has been known such that a chamber having a comparatively large capacity is communicatively connected to the compression chamber, the chamber and the combustion chamber being communicatively interconnected by a suction passage, with a carburetor disposed in the suction passage. This chamber is to store pressurized air therein thereby to inhibit an air pressure drop during a suction stroke so as to enhance the efficiency of charging. Conventionally, the capacity of the chamber has been set as large as possible, even on the order of, for example, more than 20 times the quantity of engine displacement.
However, when such a supercharged engine is employed in, for example, a small-size vehicle, such as automotive two-wheel vehicle, one problem is that it is difficult to secure necessary space for disposition of such a large-capacity chamber.
Another problem is that, in the case of a supercharged engine of the above mentioned type, if the supercharged pressure is increased when the compression ratio is set at a usual level, there will occur knocking such that the output of the engine does not go up even if the quantity of the mixture is increased.
This invention has been made in view of the foregoing situation of the art and has as its object the provision of a suction device for a supercharged engine which can prevent knocking when the engine is equipped with a supercharge mechanism and can realize a size reduction to enable use in a small type vehicle.